The present invention relates broadly to fluid pressure regulators and methods of operating the same, and more particularly to a pressure regulator having a controlled differential pressure setting capability providing improved response when utilized, for example, in batchwise gas delivery applications such as may be found in the semiconductor processing industry.
Fluid pressure regulators are used in a variety of fluid transfer applications involving the delivery or other transport of pressurized process gases or the like. Within these applications, pressure regulators are provided to deliver a flow of a pressurized gas or other fluid at a regulated outlet pressure, and to maintain that pressure at a set value generally independent of the gas flow rate. For that purpose, the pressure regulator is supplied at its inlet port by a source of fluid which typically is at a pressure substantially higher than the desired outlet pressure. The desired outlet pressure is set and the regulator automatically actuates an internal valve to adjusts the size of a variable passage between its inlet and outlet ports to minimize the offset between the actual outlet pressure and the set pressure.
As is detailed more fully in commonly-assigned U.S. Pat. Nos. 5,787,925; 5,762,086; 5,755,428; 5,732,736; 5,458,001; 5,230,359; 4,702,277; and 4,257,450, pressure regulators of the type herein involved conventionally are operated on a force balance principle. In this regard, an internal diaphragm assembly of the regulator is subjected to forces acting in opposite directions. These forces include a first force acting in a first direction and related to the pressure setting, typically developed by the manual compression of a coil or other spring, a second force acting in a second direction opposite the first direction and developed by the outlet pressure as applied to the effective area of the diaphragm exposed to that pressure. Under standard operating conditions, the first force of the pressure setting is held constant such that any variation in the inlet or outlet pressure effects a proportional change in the second, opposing force being applied to the diaphragm. The imbalance thereby created between these opposing first and second forces cause the diaphragm to deflect. This deflection is transmitted directly to the valve which cooperates with an associated valve seat to vary the open area of an orifice or other fluid passage defined between the valve and the seat and, as a result, the fluid flow from the inlet of the regulator to its outlet.
For example, a step change increase in outlet flow rate generally will tend to decrease the outlet pressure and, proportionally, the second, opposing force being applied to the diaphragm by the outlet pressure. The force imbalance thereby developed is translated to the valve element via the deflection of the diaphragm. Such deflection urges the valve element to move in a direction which increases the area of the fluid flow orifice defined between the element and its associated valve seat. This increase, in turn, effects a corresponding increase in the fluid flow rate through the regulator which ultimately balances at steady state condition wherein the decrease in the outlet pressure is modulated.
Conversely, for a step change decrease in the outlet flow rate, the flow imbalance thereby developed would have the effect of urging the valve element in an opposite direction to decrease the area of its fluid flow orifice and, proportionately, the flow rate. A new balance thus is effected in which the outlet pressure is marginally increased as compared to outlet flow prior to the step change decrease.
The above-described automatic operation illustrates that some change in outlet pressure is required to accommodate a change in outlet flow. The purpose of pressure regulation therefore is to minimize the change in outlet pressure for a given range of flow variation. In addition to outlet pressure, the response of a pressure regulator must accommodate the effect of inlet pressure changes on the regulated outlet pressure, and also the effect as the flow rate approaches zero. The latter is expressed as the ability of the pressure regulator to close under a no-flow condition.
Regarding the effects of inlet pressure changes, the inlet pressure applied to the area of the valve passage develops a force which, as aforementioned, acts in the opposite direction as that of the pressure setting force. For example, a decrease in inlet pressure results in a proportionate decrease in the force transmitted to the diaphragm assembly, with the force balance being restored by a corresponding increase in outlet pressure. Sequentially, the decrease in inlet pressure decreases the force opposing the pressure setting force which, in turn, causes the diaphragm assembly to increase the valve opening. With the flow across the valve thereby being increased, the outlet pressure is increased to a new value which again restores the force balance. As conventionally operated at inlet pressures of 30-500 psi, pressure regulators of the type herein involved typically exhibit about a 1 psi increase or, as the case may be, decrease in outlet pressure for each 100 psi change in inlet pressure.
The precise relationship between inlet pressure decrease and outlet pressure increase is determined by the ratio of the effective areas of the valve passage and the diaphragm. For a more detailed analysis of this effect, reference may be had to the present inventor""s prior U.S. Pat. No. 5,230,359, entitled xe2x80x9cSupply Pressure Compensated Fluid Pressure Regulator And Method.xe2x80x9d
Particularly for applications involving the batchwise delivery of a process gas at the point of use, there has been an expressed interest in providing for a fast start-up at the beginning of each delivery cycle. Such a start-up may be achieved when the outlet pressure of the regulator is controlled to stabilize quickly at a steady-state value as the gas flow is increased from no flow prior to the commencement of a delivery cycle, to a given delivery flow rate.
The semiconductor industry, for example, utilizes the batchwise delivery of process gases in the manufacture of integrated circuit (IC) chips or dies. In the general mass production of semiconductor devices, hundreds of identical xe2x80x9cintegratedxe2x80x9d circuit (IC) trace patterns are photolithographically imaged over several layers on a single semiconductor wafer which, in turn, is cut into hundreds of identical dies or chips. Within each of the die layers, the circuit traces are deposited from a metallizing process gas such as tungsten hexafluoride (WF6), and are isolated from the next layer by an insulating material deposited from another process gas. The process gases typically are delivered in discrete flow cycles or xe2x80x9cbatchesxe2x80x9d from pressurized supplies, thereby requiring delivery systems of a type which may be operated in alternate flow and no-flow modes.
A representative delivery system of such type is shown at 10 in the schematic of FIG. 1. Referring then to FIG. 1, delivery system 10 may be seen to conventionally include, in series, a gas supply 12, a pneumatic isolation valve, 14, a pressure regulator, 16, a pressure transducer, 18, a manual valve, 20, a mass flow controller, 22, and a pneumatic on/off valve, 24. Fluid flow through system 10 is in the direction reference by arrow 30.
Prior to the initiation of a delivery cycle, system 10 is in a start-up/stand-by or xe2x80x9cno-flowxe2x80x9d operational mode wherein pneumatic valve 24 is commanded closed, manual valve 20 is set open, and mass flow controller 22 is set to zero. At the initiation of xe2x80x9cflowxe2x80x9d or delivery operational mode, pneumatic valve 24 is commanded to open and the mass flow controller 22 is set to control flow at a desired rate. Thereupon, at the termination of the flow mode, the pneumatic valve 24 is commanded closed and the setting of the mass flow controller 22 is returned to zero. At all times during both operational modes, the pressure regulator 16 remains set at a desired regulated pressure with supply or inlet pressure being provided to the inlet 32 of the regulator and with outlet or delivery pressure being provided from the outlet 34 of the regulator to mass flow controller 22.
Indeed, within fluid systems such as system 10, there is a particular need to maintain a generally constant gas pressure notwithstanding the gas flow rate demand which varies between the operational modes of the system from low or no flow to a relatively high flow. In this regard, the flow regulating devices employed in these systems, such as mass flow controller 22, generally are highly accurate if a stable gas pressure can be maintained at the inlet of the device. However, the large pressure drops associated with changes in the flow demands of the delivery system often make it difficult to maintain a stable gas pressure and, accordingly, to assure the accuracy of the flow regulating device. Ultimately, the defect rate and yield of the process may be deleteriously affected.
Moreover, it has been observed in connection with the conventional operation of system 10 that the outlet pressure of regulator 22 begins to decrease as soon as flow is initiated in the delivery mode, and continues to decreases until it reaches a value corresponding to the setting of the regulator. The pressure decrease comprises two components, namely, a xe2x80x9ccreepxe2x80x9d component and a xe2x80x9cdroopxe2x80x9d component. The effect of each of these components may be appreciated with reference to FIG. 2 wherein a flow curve for a representative pressure regulator of the type herein involved is plotted at 40 as a function of outlet pressure (Po) versus the log of flow rate (R) for a given inlet pressure. As the flow rate increases from about 50 to 1,0000 cc/min in the direction referenced by arrow 42, the droop component is expressed as a pressure drop which is proportional to the flow rate. The creep component, in turn, is expressed as a pressure drop as the flow rate increases from zero to a small value of about 20-50 cc/min or, alternatively, as a pressure increase in the direction referenced by arrow 44 as the flow is decreased from 20-50 cc/min to zero.
The xe2x80x9ccreepxe2x80x9d of a pressure regulator therefore is defined as its ability to maintain a constant outlet pressure as the flow is decreased from a small value to a no-flow condition. In this regard, the internal valve of any pressure regulator cannot, as a result of cold flow or other deformation of the seating materials, make an absolutely fluid-tight seal in the zero flow condition. The outlet pressure of the regulator therefore is observed to increase slowly over time. The rate of increase is generally non-linear and decreases over time, i.e., it may take 30 seconds for the outlet pressure to increase by 1 psi, 3 minutes to increase by 2 psi and 30 minutes to increase by 3 psi.
The effect of creep upon the operation of a fluid system, such as system 10 of FIG. 1, is to increase the response time of the system to reach steady-state flow as the outlet pressure must decrease from a higher, creep-induced no-flow value, to a lower, operating or setpoint value determined by the regulator setting. The time necessary for the outlet pressure to reach the setpoint value of the regulator is a function of the flow rate and fluid volume between the regulator 16 and the mass flow controller 22. For example, a decrease of 2 psi, i.e., from 17 psi to a standard operating pressure of 15 psi, may require about 0.3 sec for a typical fluid volume of 8 cc and a flow rate of 200 cc/min. However, at lower flow rates, i.e., 20-50 cc/min, the response time may become significant, i.e., 1-3 sec, and even may be considered unacceptable as a response of less than 1 sec generally is desired.
A separate, but similarly important consideration is the manner in which the outlet pressure approaches a steady-state condition in response to a step change in flow rate. That is, if the outlet pressure response is not linear, but rather is oscillatory with some overshoot and recovery, it may not be possible to establish a steady state flow to the mass flow controller within the desired 1 sec interval. In this regard, the operation of mass flow controllers is known to be adversely affected by a pressure reversal as may be caused by a pressure overshoot. The greater the outlet pressure decrease from the creep-induced no-flow valve to the operating setpoint increases the potential for a pressure overshoot.
In view of the foregoing, it will be appreciated that further improvements in the design of pressure regulators for process gas delivery and other bath processes would be particularly well-received by the semiconductor manufacturing industry. Especially desired would be a regulator which provides a rapid response with no pressure overshoot from a no-flow to a flow condition of the fluid circuit, and thus economizes the use of process gases for higher yields per batch.
The present invention is directed broadly to a fluid pressure regulator construction and method of operating the same. More particularly, the invention is directed to a diaphragm-type regulator construction and method affording a controlled differential pressure setting capability providing improved response when utilized, for example, in fluid systems for the batchwise delivery of pressurized gases as may be found in the semiconductor processing industry, as well as in other applications having flow and no-flow operational modes. Such capability allows for a differential pressure setting force to be applied to the diaphragm of the regulator independently of the main pressure setting force. As a result, the regulator of the present invention may be operated in a manner which obviates or at least minimizes the effect of creep on the outlet pressure for a more rapid approach to steady-flow without pressure overshoot or other system de-stabilizing hysteresis effects.
In accordance with the precepts of the present invention, the regulator thereof is operated within a fluid system in a conventional manner except that the outlet pressure setting is determined by both a main pressure setting force, which may be manually adjustable, and an separate, differential force, which may be controlled pneumatically or by another pressure signal. In this regard, the main pressure setting force is adjusted such that the outlet flow is regulated at an outlet pressure which is incrementally less than the outlet pressure specified for the mass flow controller or other flow component of the fluid system. At about the start of the operation of the system in a flow mode, the differential force is applied to the diaphragm in the same direction as the main pressure setting force so that the fluid flow is regulated in the flow mode of the system at an outlet pressure which is about the specified outlet pressure. Thereafter, the application of the differential force is terminated at about the end of the operation of the system in the flow mode, i.e., the beginning of the no-flow mode. In this way, an ersatz creep effect is mimicked such that, over time, the outlet pressure is maintained in the no flow mode of the system at a value which is about equal to, or only marginally greater than, the specified value. Accordingly, upon the differential force being re-applied and system flow being initiated, steady-state operation may be rapidly approached with only a marginal xe2x80x9cdroopxe2x80x9d decrease in outlet pressure as the flow rate is increased and, as a result, substantially no pressure overshoot. Therefore, when utilized, for example, in the manufacture of semiconductors, the regulator and method of the present invention economizes the use of process gases for higher yields per batch.
In a preferred embodiment, the regulator of the present invention is provided to be responsive to a pneumatic or other pressure signal to apply the differential force. In this regard, the regulator includes a separate compressible spring member, which may be a spring coil, coupled in force transmitting communication with the diaphragm. For compressing the coil to apply the differential force on the diaphragm, a piston member is received within said regulator as operably coupled to the compressible member. The piston member is displaceable responsive to the pressure signal along a longitudinal axis of the regulator from a normally-biased first position to a second position effecting the compression of the compressible member to apply the differential force on the diaphragm. Advantageously, the signal may be controlled to be supplied to both the regulator and a pneumatic valve of the fluid system such that the application of the differential force is initiated at the same time as the flow mode of the system.
The present invention, accordingly, comprises the apparatus and method possessing the construction, combination of elements, and arrangement of parts and steps which are exemplified in the detailed disclosure to follow. Advantages of the invention includes a pressure regulator and method for operating the same which minimizes pressure creep when utilized in fluid systems operated in alternate flow and no-flow modes for faster pressure response and steady-state operation. Additional advantages include a regulator construction which is generally robust and economical to manufacture, and which eliminates the need for multiple stages, electronic controls, or additional valves and components heretofore necessary for more stable operation. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.